Blizzard Warning Criteria

[Robert Dewey]

Just splitting off from the NOW thread...

In respect to the blizzard warning criteria, I think Oklahoma could pass for a bit less. That's an area of the country that typically doesn't get much snow, and when it does snow, I think it tends to shut everything down. As for MKX, they were reporting gusts over 35mph, but I'm not sure of the duration and haven't checked visibility.

Looking back in time, I don't think the Jan 1999 blizzard met criteria at my specific location here in Oakland county, as winds were barely making the 35mph mark. However, it *seemed* like a blizzard to many in the area because of the heavy snowfall rates (visibility under 1/4 mile for most of the event, with periods of blinding snow / thunder).

Rather than change the criteria, I think a better assessment of the situation needs to be made. If upstream and local METARs are reporting a solid 35knt wind gusts and analysis / models continue to show good wind and snow potential, then a blizzard warning would be more suitable.

 

[Jeff Snyder]

Might be time for a new thread - but I wonder if we need to consider changing blizzard criteria. This storm did not meet criteria, and a quick check didn't find any sites in OK yesterday that met either...

All quiet around mid-Michigan, we picked up 1/4-1/2" ice with no major problems, roads were icy for a bit in the middle of the night but primarily just slush thanks to the very warm wx we've been having.

Not to drag this beyond a NOW thread, but I believe the NWS criteria for a blizzard is "where both the 10m wind speed is >=30kts and surface visibility is < 1/4 mile - in falling snow or ice pellets for at least three hours" (from the HPC website)". If that's the case, I can't imagine some places in northern OK didn't meet that yesterday (particularly the first half of the day). I know I saw numerous mesonet obs with gusts >40mph, and visibility in many places in the heavy snow bands was <1/4 mile. I suppose there may have been a problem with three continuous hours of those conditions given that the heavy snows were banded, but those conditions were at least off-and-on for more than a few hours.

Here in Edmond, OK, I'd estimate approx 5" of snow/sleet, though I haven't measured. Many of the nearby roads are slick, but certainly not impassable or terrible. I was a little disappointed that OUN didn't release as many LSRs for storm totals through the course of the events... I saw a dozen or so yesterday, but that pales in comparison to offices like EAX or SGF, which put out the same amount in about 2 hours, which made keeping track of snowfall totals much easier.

 

[Brian Stertz]

Yeah true enough Jeff...some NWS offices crank out the info and some just stay clammed up. A good tool now is the TV station blogs...this was pretty good information in most cases, especially the reports that were coming in where the thundersnow happened. But back to the thread...blizzards affect different areas in different ways. Out in Wyoming, these are probably about every other winter storm that comes along. In Oklahoma/S.Kansas like yesterday...the conditions got pretty wicked in those deep snow bands. Plus add in the flat land ares up there, the wind just roars across the barren wheat fields. I've driven through that area in a similar event and it was scary to come up on other cars appearing out of nowhere. Blizzard always conjurs up in non-met people's minds that the most horrific winter storm is in progress. Most people have NO idea what a blizzard is.

 

[Robert Dewey]

Blizzard always conjurs up in non-met people's minds that the most horrific winter storm is in progress. Most people have NO idea what a blizzard is.

That's the intention of a blizzard warning - it supposed to capture the public's attention and alert them to the fact that they shouldn't be driving unless there is an emergency. In the most severe blizzards, people are even advised to stay indoors (there are cases where people get disoriented and lost on their own property).

 

[rdale]

First - the official definition from NWS 10-513:

3.1 Blizzard. A blizzard means that the following conditions are expected to prevail for a
period of 3 hours or longer:
a. Sustained wind or frequent gusts to 35 miles an hour or greater; and
b. Considerable falling and/or blowing snow (i.e., frequently reducing visibility below
1/4 mile).
Although there is no set temperature requirement for blizzard conditions, the life-threatening
nature of the low temperatures in combination with the other hazardous conditions of wind,​

snow, and poor visibility increases dramatically when the temperature falls below 20*F.


The public refers to any big winter storm as a blizzard... Blizzard warnings are RARELY (if ever) successfully warned in advance, because the criteria are incredibly hard to meet let alone forecast. They usually are issued during an event when mets see the numbers start to go up - but by then, everybody knows about it, they are already indoors unless they have to go out, and if they have to go out - it doesn't matter!

So would relaxing the criteria (not sustained for 3 hours, or maybe not so tight on vis since we're relying on all automated vis sensors these days) be a service to the public?

 

[Rick Smith]

NWS guidelines also say this...

During early and late season storms, or in places where winter weather is rare, WFOs may issue winter weather warnings based on significant public impact events which do not meet local warning criteria. For example, if a storm (such as one with heavy, wet snow or a mixture of snow, freezing rain and sleet) is forecast to significantly affect transportation, commerce or electrical power service, then the event warrants a warning.

...and in many cases the need to get a message out will outweigh the sometimes arbitrary guidelines. In the case of the Oklahoma blizzard warnings, criteria was likely met in several locations for short periods of time. However, the desired effect of the message was to get people's attention and to alert them that a potentially life-threatening event was underway.

I can tell you from first hand experience that you can have treacherous, dangerous driving conditions even if the winds are only gusting to 30 MPH.

Rick

 

[Karen Politte]

Yeah I was a bit perturbed too at the lack of real-time reports from OUN yesterday. I'm sure that most people have far too much going on to bother yadda yadda - but it seems like in events past there was an overabundance of reports of "such-and-such-a-place has received .15" of ice so far.......". Last night - during the first REAL event in a while - there was nothing. Just a Graphicast image of the "expected" accumulations over the next 24 hours.

I was also interested - on my side of the fence - to watch and see how LZK attempted to forecast the cold air moving down behind the front. I think their forecasts would have panned out if it had not been for the pesky low that developed along the front by mid-afternoon slap-bang in the middle of southern Arkansas. This meant that areas in southeast Tejas froze before Conway and LZK did......pretty pathetic! I can only assume that this was due to a combination of the low south-east of us which kept us bathed in the (comparatively) tropical conditions of some wrap-around heat and moisture, and the wafer-thin layer of cold air that was trying to trundle up and down the Ozarks towards us........poor cold air. It must be knackered.

KL

 

[Robert Dewey]

The public refers to any big winter storm as a blizzard... Blizzard warnings are RARELY (if ever) successfully warned in advance, because the criteria are incredibly hard to meet let alone forecast. They usually are issued during an event when mets see the numbers start to go up - but by then, everybody knows about it, they are already indoors unless they have to go out, and if they have to go out - it doesn't matter!

So would relaxing the criteria (not sustained for 3 hours, or maybe not so tight on vis since we're relying on all automated vis sensors these days) be a service to the public?

I think a better method of awareness would be to use blizzard watches for events that appear as though they could meet the criteria. For example, if the event is 12 - 18 hours away and there is good agreement that there will be a combination of high wind in excess of 35knts and heavy snow, then that might be a good flag for blizzard watches.

I think the public perceives a blizzard to be worse than "a major winter storm". The watches would alert the public and leave a bit more confidence on the forcasters plate. Of course, they would still need to be used sparingly or the watches/warnings would end up much like SVR watches/warnings.

 

[rdale]

WFOs may issue winter weather warnings based on significant public impact events which do not meet local warning criteria.

Agreed - but that does not apply to blizzards. That refers to issuing a Winter Storm Warning instead of an Advisory - it does not allow for reduction of the blizzard criteria.

 

[rdale]

I think a better method of awareness would be to use blizzard watches for events that appear as though they could meet the criteria.

That is what is used today...

Blizzard Watch - Conditions are favorable for a blizzard event to meet or​

exceed Blizzard Warning criteria in the next 12 to 48 hours.

What I'm saying is that it is VERY difficult to forecast that winds will be > 35mph for 3 hours AND at the same time reducing vis to 1/4mi or less. Very. Look how bad some forecasters did with basic snowfall in this past storm, and now you throw in 24 hours advance worth of pinning down where the isolated extreme snow will happen. Can't do it...

 

[Robert Dewey]

Rob,

I'm not sure I understand. Are you saying the criteria should be lowered? Or are you for a higher criteria?

I know high wind watches and warnings are issued with a fair amount of accuracy. If you have a potential for heavy snow and you also meet high wind watch criteria, then I would say a blizzard watch would be a good option. The quarter-mile visibility is a result of the wind + snow, so that would be your forecast starting point.

Even with the NWS "having" blizzard watches available, they aren't used much outside of Alaska. Even last year's Northern Plains blizzard was "missed" by a blizzard watch; models consistently predicted +45knt surface winds and very heavy QPF in 20F temps. Why no blizzard watch? It was quite obvious that those conditions could be met.

With that said, the prediction would still be difficult for marginal events. If the NAM is showing only 35knts at one timestep, then what? Winter storm watch, or blizzard watch? Most of the events we see across continental US would be "marginal", so I guess there really is no benefit ;-)

 

[rdale]

Lowered... Unless someone found a hidden spot - none of the blizzard warnings with this storm , issued in WI & OK, verified with the current criteria.

 

[Joel Wright]

They could always go with a blizzard warning for slightly lowered thresholds like some of you guys have suggested above; and to keep the "mystique" of a really bad storm that rarely happens (like the current blizzard threshold has) go with a super blizzard warning for REALLY bad blizzards.

Something like this..
For a blizzard warning: winds of 25mph sustained or frequent gusts above 30mph, combined with heavy snow with visibilities <3/8 mile for 3hrs consectutively, or numerous periods within 6hrs.

For a super blizzard warning: winds of 35mph sustained or frequent gusts above 45mph, combined with heavy snow and visibilities at or <1/4 mile for a minimum of 3hrs.

 

[Mike Umscheid]

Lowered... Unless someone found a hidden spot - none of the blizzard warnings with this storm , issued in WI & OK, verified with the current criteria.

I disagree, Rob. Below are the Enid obs. The area of north central Oklahoma certainly saw frequent gusts at or above 35 mph for most of the day on the 30th. Even though the visibility is only reported as "only" 1/4SM... ASOS and AWOS sensors rarely report "M1/4 SM". These obs from 15z to 21z would verify 6-hour blizzard, based solely on the current criteria. Perhaps Rick Smith can jump in on this... but the observations, to me, would support at least a 6-hr blizzard for parts of NC Oklahoma per NWS definition. I've done a lot of blizzard researching for western Kansas since I moved down here... and the Visibility reported by automated stations are usually not low enough from my experience, in very strong wind+snow situations out on the high plains. [SIZE=-1]

METAR KWDG 301455Z 33025G35KT 1/4SM SN BLSN VV001 M08/M09 A3017
METAR KWDG 301550Z 34020G32KT 1/4SM SN BLSN VV001 M08/M09 A3019
METAR KWDG 301650Z 33020G30KT 1/4SM SN BLSN VV001 M08/M09 A3015
METAR KWDG 301750Z 34020G32KT 1/4SM SN BLSN VV002 M08/M09 A3015
METAR KWDG 301850Z 33022G36KT 1/4SM SN BLSN VV001 M08/M09 A3017
METAR KWDG 301950Z 33020G29KT 1/4SM SN BLSN VV002 M08/M09 A3010
METAR KWDG 302050Z 33020G31KT 1/4SM SN BLSN VV002 M07/M09 A3007[/SIZE]
Mike U

 

[rdale]

While it's nice to 'infer' that vis was < 1/4mi, and I don't disagree with that, the fact remains that the observations don't meet current criteria...